Superhardened steel and process for producing the same



Patent Feb. 5, 1924.

" uurreo STATES ice.

AXEL GUSTAIF EMANUEL HULTGREN, OF GOTTEHBORG, SWEDEN.

SUPERHARDENED STEEL AND PROCESS FOR PRODUCING THE SAME.

No Drawing.

To all whom it may concern:

Be it known that I, AXEL GUs'rAr EMAN- UEL HULTGREN, a subject of theKing of Sweden, residing at Gottenborg, Sweden, have invented certainnew and useful Improvements in Superhardened Steel and Processes forProducing the Same, of which the following is a specification.

This invention relates to a new product '10 and the method ofproducingthe same, and to superhardening heat treated hardened metal articles. Itis peculiarly adapted for mechanically superhardening the metal at andadjacent the surface of articles which have been hardened by heattreatment and preferably ground and polished or otherwise;

previously reduced to approximately their finished form.

There are many practicable applications 3:) to which this invention maybe applied, one of which being the interengaging parts of anti-frictionbearings, as for instance, the surfaces of the race grooves of ball andI roller bearings, and also the .sur-

faces of the rolling elements, namely the balls and the rollers. 7

Broadly stated, this inventionhas to do with cold working an article ofhardened steel to make its surface still harder.

It has been well known since the earliest ages that many metals whenthey are in a soft condition and cold can be mechanically hardened bythe application of pressure, or a series of blows, to the surface. Thisprimitive method was employed on metals not capable of being hardened byheat treatment as now practiced upon steel. I have discovered that metalwhich has been brought to a high state of hardness by quenching fromproper hardening temperature, which in some instances is followed bytempering, may be still further hardened, or more properly superhardenedby cold working to an extent which produces a permanent deforma-- tion.

By the term heat treatment, as used in this specification and theappended claims, is meant that effect produced upon the steel by more orless suddenly cooling from a temperature above the transformationtemerature. This statement is made not to imit the scope of the materialworked upon,

but to simplify the description and to prevent equivocation arising froma meaning 1 sometimes placed upon t e term heat treat- Applieation filedJune 15, 1920. Serial 1W0. 389,182.

ment to include not only the hardening but also the softening orannealing.

In many industries, such as the manufacture of the rings and the rollingelements for ball and roller bearings, the parts are not heated a secondtime to a temperature sufiiciently high to come under the more technicaldefinition of tempering. In the heat treatment to which theyaresubjected they are heated to a fairly high degree of temperature,submerged in a cold quenching bath and then soaked for quite an extendedperiod in a warm bath of only sufficient temperature to remove or modifythe internal stresses created by the quenching.

One illustration of an article so made, and the method of treating thesame is a deep groove single row ball bearing. The rings of this areformed in some well known or other suitable manner, they are then heatedto approximately 1500 degrees Fahrenheit, .and' quenched in a bath ofapproximately at-' mospheric temperature, and removed from this bath andimmersed for approximately an hour in a bath of oil heated to about 300degrees Fahrenheit. It is to be understood that this is merely anillustration and cited to assist in the general understanding of thisinvention. In those articlesin which it is not. necessary to remove theinternal' hardening stresses, the step of soaking in. the tempering bathmay be eliminated, and also that in those articles where it is desiredto have greater toughness thanthat produced by the recited method, themodifying heat may be of such magnitude that the resultant may betechnically described as tempering.

In the case of a ball bearing, after the parts are heat treated themajor surfaces are ground and polished, and the inner and guilzier ringsassembled with a complement of Each individual ball bearing is designedby its maker to carry a certain amount of load, and a radial bearing isdesigned to carry a certain amount of pure radlal load or a certainamount' of pure axial or thrust load or certain combinations of these,such loads to be carried-for extended intervals over a long period oftime. The bearing, however, and its different parts is generally capableof sustaining an enormous amount 7 of overload for a brief interval.When it is, therefore, desired to mechanically superharden the bearingsurfaces of the elements occupied normally by the balls wearing away bythe balls 1 which resultant formation superhardened, or with whatever ofa ball bearing it is purposed by this invention to overload the bearingwhile rotating. As an illustration, the bearing is rotated for a shorttime while loaded to about ten times its rated capacity and exerts apressure upon the surfaces being treated beyond their elastic limit. Theeffect of thus working the surface of the rings at the race grooves bythe contact of the balls while rolling under heavy overload is to effectpermanent deformation and harden the metal at and adjacent the surfaces.While engaged in'this rolling of the race rings the balls themselves arere-acted upon' and their metal at and adjacent the surface is similarlypermanently deformed and hardened. The result is that the ball bearingwhen subsequently subjected to the loads which it is normally designedto carry presents engaging surfaces between the rolling elements or therelatively moving elements which are of high durability thereby addinggreatly to the length of life of the entire structure. In ball bearingsthere is no such thing as the grooves and balls gradually and uniformlyrolling over the race ways of these grooves. Under ideal conditionsthere is no sliding friction between the parts and absolutely no wear orother destructive action. -Ideal conditions, however, rarely exist orpersist for long periods of time. Overload and shock loads bring aboutdestructive tendencies which generally result in fatiguing the surfacesare in rolling engagement with the of mlnute fatigue cracks which causeflaking of the surfaces. Superhardened surfaces such as are hereindescribed present a structure which has great power of resistance andwhich can endure all the abusive conditions usually encountered withoutfatiguing the metal.

In carrying out this method according to the illustrative example aboveset forth of superhardening the arts of an individual ball bearing ithas been assumed that the ball bearing will be assembled prior to beingsubjected to this treatment, and will remain as originally assembled. Itis, however, quite desirable in many instances to superharden thesurfaces upon which the balls roll by other rolling elements thantheballs which enter into the structure when put into use. This may beaccomplished by specially formed rollers applied to the rings individually or to rollers in the form of balls be? tween such rings 'andoccupying the position therein. Those superhardened rings are thenassembled either with" balls otherwise especiallya requirements of thebearing in use demand. There are many'uses to which superhardened ballsare put other than as the rolling elements between innerand outer racerings balls the one of these is the hardness testing method of Brinnellsmachine. A tough hard ball is a thing which is desired in this testingmethod especially in testing hardened steel,

in which case the generally used Brinnells ball, having the samehardness as the steel to be tested, is to som extent flattened out bythe pressure, thus giving an incorrect test result. In; manufacturingsuperhardened balls according to my invention a ball made of the .propersteel and brought to the highest practicable hardness by heat treatmentis then subjected to cold working to harden it to such an extent thatwhen in the hardness test it is subjected to the pressure its sphericalform will be practically unalterable. The ball must also be of suchcharacteristics that repeated applications of testing pressure will notpermanently deform it or break it.

In the manufacture of articles for certain purposes it has been founddesirable to subject the worked article to a tempering heat preferably alow tempering heat for relieving the stresses of workin In themanufacture of suchv articles as razor blades and analogous articles itmay be found expedient to grind and polish por- .tions which have beensuperhardened and this work will be done in proper sequence with thesecond tempering where this is practiced. It might be in the case ofrazor blades that the grinding would precede the second tempering, andthe polishing succeed it.

It is to be understood that the invention is applicable to a wide rangeof manufactured articles, and that the examples selected forspecific'description are illustrative of a wide range of subject matter.It is quite obvious that not only is it desirable to superhardensurfaces which are intended to support loads and bodies which are to beheld against deformation when loaded, but also edged tools of variousdescriptions which are required to retain a very fine edge.

I claim as my invention,

1. The method which consists of forming a steel article, then hardeningthe same, and then subjecting such article to a rolling pressure forsuperhardening the steel thereof at and adjacent the surface.

2. The method which consists of forming an article of steel, thenhardening the article by quenching from a proper hardening surfacethereof. 7

3. The method which, consists of forming an article of steel, thenhardening the article .by quenching from a proper hardening temperature,then grinding'and polishing 'certainfaces thereof, then subjecting suchfaces msaaaa temperature, and then subjecting such ar-- ticle to arolling pressure for superhardening the metal at and adjacent the saidsurface thereof.

5. The method which consists of forming an article of metal, thenhardening the article by quenching from a proper hardening temperature,then subjecting such article to a rolling pressure for superhardeningthe metal at and adjacent the said surface thereplf, and then drawing ata low tempering eat.

6. That improvement in the art of treating metal which consists inhardening a formed metal article by heat treating the same, and thensuperhardening the surface thereof by the application of a series ofblows or the equivalent thereof.

7. That improvement inthe art of treating metals which consists informing a metal article, heat treating the article for hardening,cleaning certain surfaces thereof, then subjecting said surfaces to arelative rolling action thereby superhardening the said surface.

I 8. The method which consists in forming bearings which consists informing the race rings and balls and hardening the same by heattreatment, then assembling the bearing and then subjecting the bearingto an excessive overload while rotatingthe bearing for the purpose ofsuperhardening the metal at the track grooves and for superhardening themetal of the balls at-the surface.

11. The method of manufacturing steel balls which consists in formingthe balls and hardening the same by heat treatment, then assembling theballs in bearing rings, and then subjecting the bearing to an excessiveoverload while rotating the bearing for the purpose of superhardeningthe metal of the balls at the surface.

12. The method of forming superhardened balls which consists in formingballs of suitable metal, then heat treating the balls for hardening thesax'ne, then subjecting the heat treated hardened balls to a rolling,motion between two hardened surfaces for superhardening the balls.

13. As an article of manufacture a steel ball formed of heat treatedhardened metal, and having the metal at and adjacent its surfacesuperhardened by rolling and pressure.

14. As an article of manufacture a roller bearing comprising a pair ofrace rings and a series of rollers therebetween, the race rings androllers being formed of heat treated hardened steel, and the engagingsurfaces thereof being superhardened by rolling pressure.

15. A ball formed of tempered steel having the metal at and adjacent itssurface permanently deformed and superhardened.

16. The method which consists in forming an article of steel, thenhardening and tempering the said steel, and then subjecting the surfacethereof to a force to permanently deform and superharden the same.

\ 17. The method of manufacturing roller bearings which consists informing race rings and hardening the same by heat treatment, thenassembling the rings with rollers therebetween, and then subjecting theassembled bearing to an excessive overload while rotating same for thepurpose of hardening the metal at the roller track.

In testimony whereof, I have afiixed my signature hereto.

AXEL GUSTAF EMANUEL HULTGREN.

